@@ -9,8 +9,14 @@
* ---------------------------
* The change attribute (i_version) is mandated by NFSv4 and is mostly for
* knfsd, but is also used for other purposes (e.g. IMA). The i_version must
- * appear different to observers if there was a change to the inode's data or
- * metadata since it was last queried.
+ * appear larger to observers if there was an explicit change to the inode's
+ * data or metadata since it was last queried.
+ *
+ * An explicit change is one that would ordinarily result in a change to the
+ * inode status change time (aka ctime). i_version must appear to change, even
+ * if the ctime does not (since the whole point is to avoid missing updates due
+ * to timestamp granularity). If POSIX mandates that the ctime must change due
+ * to an operation, then the i_version counter must be incremented as well.
*
* Observers see the i_version as a 64-bit number that never decreases. If it
* remains the same since it was last checked, then nothing has changed in the
The i_version field in the kernel has had different semantics over the decades, but we're now proposing to expose it to userland via statx. This means that we need a clear, consistent definition of what it means and when it should change. Update the comments in iversion.h to describe when the i_version must change. Cc: Colin Walters <walters@verbum.org> Cc: NeilBrown <neilb@suse.de> Cc: Trond Myklebust <trondmy@hammerspace.com> Cc: Dave Chinner <david@fromorbit.com> Link: https://lore.kernel.org/linux-xfs/166086932784.5425.17134712694961326033@noble.neil.brown.name/#t Signed-off-by: Jeff Layton <jlayton@kernel.org> --- include/linux/iversion.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)